Hello, you guys. Here is the deal. I'll be starting up my Part 15 station
Hello, you guys. Here is the deal. I'll be starting up my Part 15 station
with the next few weeks if all goes well. I came up with something here, but I'm not sure if its in compliance or not. If any of you can help me
with this. We know that the Procaster AM Transmitter comes with an aluminum antenna. My question is....what if I replaced the aluminum antenna with a copper antenna of the same length and width...would that
increase the range any...and would I still be in compliance with Part 15?
Jack63
After some suggestions made here, I have been considering doing the same thing with a Rangemaster, except to actually use a wider diameter copper pipe which is the same length as the whip antenna.
The wider diameter provides more surface area, which inturn improves the signal. Doing this would still be in compliance since you are staying within the 3 meter rule..
The only drawback is that it would void the certification of your Procaster..
Like I said, I'm considering it too, but as of yet have not made a definite decision.
It kind of bothers me to void the certification.
Check out this thread: http://www.part15.us/index.php?q=node/2746
The comments there are from the veteran part15ers who actually know what their talking about! I'm just repeating what I heard
It's my understanding that you can use any 108 inch whip with the Rangemaster. I don't see why a copper metal tube that screwed into the 3/8 inch antenna fitting would void the certification, as long as you keep it within the legal length, and as long as you don't make any modifications at all to the transmitter (including replacing that fitting).
The Procaster might be another matter, as the antenna is an integral part of the complete certified unit, and to modify it would likely void the certification.
In one sense, you could consider them to be the same, but the reality confronting most users is that even a certified unit operating in the wild could be made to propagate a signal an FCC agent might consider illegal.
I feel it's important to note that in the end, it's the operator who is responsible for compliance, not the manufacturer.
This is a good spot to ask my question since a 4-Element Cage Monopole is one low budget way to increase the bandwidth of an antenna without spending so much money for wide copper pipe.
The 4-Element Cage Monopole is simply made by hanging 4 wires in a cube style pattern, an even distance apart, ten feet high, completely tied together at the bottom where the transmitter antenna feed connects, and not connected to anything up at the top. Basically, it's four parallel antennas that act like a pipe of similar thickness.
My question is, how widely separated can the 4-elements be before they begin having phase distortion.
Another way to ask is, how thick can a thick-pipe antenna be.... perhaps wide as a petroleum barrel?
There must be a limit to width vs. performance, but what would that be?
If you start with this formula
And continue with the calculations here
you get some interesting outputs
At 9.8 feet long, a 1" diameter radiating element would seem to need about 260 uH of inductance for a match, or an air coil with about 70 turns on a 3" X 3" coil form
A radiating element 24" in diameter would only need around 75 uH of inductance for a match and around 38 turns on the same coil form.
A radiating element 48" in diameter would only need around 34 uH of inductance for a match and around 25 turns on the same coil form.
It's possible there might be a discernible benefit to cutting the number of coil turns nearly in half or more, perhaps greatly reducing coil resistance.
The cage monopole would seem to be an attractive way to get a 24" - 48" virtual radiator.
It's not likely the formulas are accurate at the fringes of the parameters but just for fun I solved for 0 uH needed for a match. A 9.8' tall element would need to be around 85 inches (about 7 feet) in diameter for the formula to calculate 0 uH.
It's my understanding that you can use any 108 inch whip with the Rangemaster. I don't see why a copper metal tube that screwed into the 3/8 inch antenna fitting would void the certification, as long as you keep it within the legal length, and as long as you don't make any modifications at all to the transmitter (including replacing that fitting).
The more I consider Artisan Radio's comment, the more it makes perfect sense..
I've purchased a Rangemaster on two occasions, but neither time received a antenna with it.
While you do have an option of including the 102" whip with you order, it's advised to just go to Radio Shack for one due to the fact that it takes special packaging and must be shipped separately and it increase your cost.
What's more, is now, from the Rangemaster site you have the new option of purchasing a 102" telescoping Antenna, which does not need special packaging or separate shipping..
My point is this:
A 102" stainless steel whip is good with the certification.
A 102" fiberglass whip does not void certification.
A 102" telescoping antenna does not void certification
Why then would a 102" copper pipe antenna be any different?
By the way - Jack63, to answer your question again, lest there be any confusion..
Procaster AM Transmitter comes with an aluminum antenna. My question is....what if I replaced the aluminum antenna with a copper antenna of the same length and width...would that increase the range any...
Yes, it would increase the performance, and inturn provide a better signal. The bigger around the copper antenna is the better.
and would I still be in compliance with Part 15?
Yes your transmitter would still be in compliance - you would still be legal to transmit that way.
There remains the question on if it would void the FCC certification of your Procaster or not, but it's not illegal to void the certification either...
Using the 1950 exploitation film title style 🙂
Combining some of the thoughts on this thread, a larger diameter antenna will have more bandwidth and will reduce the inductance needed for a match and a cage monopole might be a quick, inexpensive way to achieve a larger diameter.
A web page here
www.smeter.net/antennas/wire-cage-dipole.php
Offers a DOS applet and gives some additional info about cage antennas.
Playing around with that applet, it appears that the beneficial effects drop off quickly after five wires arranged in a 12" diameter cage.
To the left is a sketch of a 12" diameter, 5 wire cage monopole using a solid metal top to sneak in a bit of a capacitive hat and a coat hanger wire ring at the bottom with 18 ga. magnet wire for the vertical sections. It's not to scale, in real life it would be a bit taller and skinnier but it's a little easier to view in this shape.
Using the antenna capacitance and inductance calculations referred to above and adding 5 pF (pure guess) for the 12" hat, the antenna would only need around 100 uH for a match, or around 50 turns on the 3" X 3" air coil form with a ground tap 10 turns from the bottom.
Interesting theoretical loaded wire cage monopole with a more forgiving bandwidth and lower coil resistance - hmmm.... 🙂
Personally I would not go copper unless my system was in a protected area. Why? Just because of the copper thieves.
Yeah i know things are tough because of the economy but really why make your gear a target for theft? I understand the reasoning behind using copper believe me, nothing preforms as well for RF applications than copper but if they want the pipe and can get to it who's to say they wont go after the Transmitter you paid big bucks for?
Just throwing that out there.
"Personally I would not go copper unless my system was in a protected area. Why? Just because of the copper thieves."
So ... easy fix: Paint it. White and red bands would look cool.
Paint it. White and red bands would look cool.
Right, and you could offer Part15 compliant haircuts on the side
Nice idea, but no solution here. I'm afraid it wouldn't hold up during winter storms.
Unless mounted upon a form that could be bolted down. What would a PVC form do to the signal? Won't the FCC consider all the wires radiators? With 4 elements the thing could only be 3' in length ... so there goes your advantage.
Also, how do you tune it? At our flea power, I think it will still need matching to peak resonance.
OK for experiments, though. Expand your experience ... try anything! 😉
Putting wires in parallel does not increase the length of an antenna. For a comparison, in a single wire antenna you can use stranded wire. Does every strand count toward the length? No. Litz wire is an even better example. The word monopole is a big clue: it means "one pole."
Thank you SCWIS for putting the info about five wires being the practical limit for a cage antenna. I have tried both a 3 and 4-element, and was able to detect a very slight improvement with 4, watching an S-meter go up just a bit higher. That was an FM test. I also found that indoor stability of the signal is very solid compared to one wire. I can move around without ever disturbing the signal.
Now, based on my FM testing and this informative thread, we will try a 5-wire cage monopole for AM.
"Putting wires in parallel does not increase the length of an antenna."
Aha! You're right! But it still might not be that efficient. Would it be considered and array (also illegal IIRC)? What will the effect of different diameters do to it? How will you ground it? How will you tune it? Will a cone at top and bottom help or hinder? How will you stabilize it? How much will the eddies between elements affect it, and what about phasing between them? Why wires. i.e., wouldn't four (or five) 1/2" pipes be more physically stable with less resistance (seems like setting wires out in the breeze will flop around a lot)?
The cage has been around for awhile, but I have no info about using one in a Part 15 flea-powered installation ... so hurry up and build one so we can all stand in awe ... or laugh ourselves off our stools, as the case may be 😉
I await with bated breath ...
Also, I meant 2.5 ft/leg (now non-sequitur).